Tetrafluoroethylene/perfluoro(alkyl vinyl)ether (TFE/PAVE) melt-fabricable copolymers are widely employed in industrial injection molded goods and wire insulation applications. Their unique combination of chemical stability and high-temperature properties make them a preferred material for a wide range of injection molded parts, extruded pipe and tubing, and vessel liners.
TFE/PAVE resins are produced by aqueous polymerization (U.S. Pat. No. 3,635,926), or polymerization in a perhalogenated solvent (U.S. Pat. No. 3,642,742) or hybrid processes involving both aqueous and perhalogenated phases (European patent application No. 83104138.9). Free radical polymerization initiators and chain transfer agents are used in these polymerizations and have been widely discussed in the patent literature. For example, persulfate initiators and alkane chain transfer agents are described for aqueous polymerization of TFE/PAVE copolymers (U.S. Pat. No. 3,635,926). Fluorinated peroxide initiators and alcohols, halogenated alkanes, and fluorinated alcohols are described for nonaqueous (U.S. Pat. No. 3,642,742) or aqueous/nonaqueous hybrid polymerizations (European application No. 83 104138.9). The particular choices of initiator and chain transfer agent are dictated by the process conditions selected (temperature and reactant concentration) and the resin properties (viscosity and molecular weight distribution) desired.
The selections of the initiator and chain transfer agent dictate the end groups on the polymer chain. Persulfate initiators are known to give --COOH end groups in aqueous polymerization. If a polymerization buffer, such as an ammonium salt, is employed, --CO.sub.2 NH.sub.4 end groups are obtained which convert to --CONH.sub.2 ends during thermal conditioning. If methane is used as chain transfer agent, --CF.sub.2 H and --CF.sub.2 CH.sub.3 ends will also be present in the resin.
In a nonaqueous polymerization (or aqueous/nonaqueous), peroxides such as (ClF.sub.2 C(CF.sub.2).sub.n COO).sub.2 may be used as initiators, leading to --CF.sub.2 Cl end groups. If methanol is used as the chain transfer agent, --CF.sub.2 H and --CF.sub.2 CH.sub.2 OH end groups will also be present. In this type of polymerization, --COF end groups are also formed by unimolecular rearrangement of a PAVE radical on a growing chain, i.e. ##STR1##
While the perfluorinated chains of the TFE/PAVE copolymers have extremely good thermal stability and chemical inertness, the end groups of the TFE/PAVE copolymers described above can be chemically reactive and thermally unstable.